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use crate::{
    syntax_node::GreenNode, ParserError, SmolStr, SyntaxKind, SyntaxTreeBuilder, TextRange,
    TextSize, TreeSink,
};
use rslint_lexer::Token;
use std::mem;

/// Structure to convert events to a lossy syntax tree which does not preserve whitespace.
#[derive(Debug)]
pub struct LossyTreeSink<'a> {
    text: &'a str,
    tokens: &'a [Token],
    text_pos: TextSize,
    token_pos: usize,
    state: State,
    inner: SyntaxTreeBuilder,
    errors: Vec<ParserError>,
}

#[derive(Debug, Clone, Copy)]
enum State {
    PendingStart,
    Normal,
    PendingFinish,
}

impl<'a> TreeSink for LossyTreeSink<'a> {
    fn consume_multiple_tokens(&mut self, amount: u8, kind: SyntaxKind) {
        match mem::replace(&mut self.state, State::Normal) {
            State::PendingStart => unreachable!(),
            State::PendingFinish => self.inner.finish_node(),
            State::Normal => (),
        }
        self.eat_trivias();
        let len = TextSize::from(
            self.tokens[self.token_pos..amount as usize]
                .iter()
                .map(|x| x.len)
                .sum::<usize>() as u32,
        );

        let range = TextRange::at(self.text_pos, len);
        let text: SmolStr = self.text[range].into();
        self.text_pos += len;
        self.token_pos += amount as usize;
        self.inner.token(kind, text);
    }

    fn token(&mut self, kind: SyntaxKind) {
        match mem::replace(&mut self.state, State::Normal) {
            State::PendingStart => unreachable!(),
            State::PendingFinish => self.inner.finish_node(),
            State::Normal => (),
        }
        self.eat_trivias();
        let len = TextSize::from(self.tokens[self.token_pos].len as u32);
        self.do_token(kind, len, false);
    }

    fn start_node(&mut self, kind: SyntaxKind) {
        match mem::replace(&mut self.state, State::Normal) {
            State::PendingStart => {
                self.inner.start_node(kind);
                return;
            }
            State::PendingFinish => self.inner.finish_node(),
            State::Normal => (),
        }

        let n_trivias = self.tokens[self.token_pos..]
            .iter()
            .take_while(|it| it.kind.is_trivia())
            .count();

        self.eat_n_trivias(n_trivias);
        self.inner.start_node(kind);
    }

    fn finish_node(&mut self) {
        match mem::replace(&mut self.state, State::PendingFinish) {
            State::PendingStart => unreachable!(),
            State::PendingFinish => self.inner.finish_node(),
            State::Normal => (),
        }
    }

    fn errors(&mut self, errors: Vec<ParserError>) {
        self.errors = errors;
    }
}

impl<'a> LossyTreeSink<'a> {
    pub fn new(text: &'a str, tokens: &'a [Token]) -> Self {
        Self {
            text,
            tokens,
            text_pos: 0.into(),
            token_pos: 0,
            state: State::PendingStart,
            inner: SyntaxTreeBuilder::default(),
            errors: vec![],
        }
    }

    /// Make a new tree sink but start the sink at a specific token, this is used for making completed markers
    /// into AST nodes for rules which need them.
    ///
    /// # Panics
    /// Panics if the token start does not line up to a token's start index or is out of bounds
    pub fn with_offset(text: &'a str, tokens: &'a [Token], token_start: usize) -> Self {
        let mut len = 0;
        for (idx, tok) in tokens.iter().enumerate() {
            if len == token_start {
                return Self {
                    text,
                    tokens,
                    text_pos: (len as u32).into(),
                    token_pos: idx,
                    state: State::PendingStart,
                    inner: SyntaxTreeBuilder::default(),
                    errors: vec![],
                };
            }
            len += tok.len;
        }
        panic!("Token start does not line up to a token or is out of bounds")
    }

    pub fn finish(mut self) -> (GreenNode, Vec<ParserError>) {
        match mem::replace(&mut self.state, State::Normal) {
            State::PendingFinish => {
                self.eat_trivias();
                self.inner.finish_node()
            }
            State::PendingStart | State::Normal => unreachable!(),
        }

        (self.inner.finish(), self.errors)
    }

    fn eat_trivias(&mut self) {
        while let Some(&token) = self.tokens.get(self.token_pos) {
            if !token.kind.is_trivia() {
                break;
            }
            self.do_token(token.kind, TextSize::from(token.len as u32), true);
        }
    }

    fn eat_n_trivias(&mut self, n: usize) {
        for _ in 0..n {
            let token = self.tokens[self.token_pos];
            assert!(token.kind.is_trivia());
            self.do_token(token.kind, TextSize::from(token.len as u32), true);
        }
    }

    fn do_token(&mut self, kind: SyntaxKind, len: TextSize, skip: bool) {
        let range = TextRange::at(self.text_pos, len);
        let text: SmolStr = self.text[range].into();
        self.text_pos += len;
        self.token_pos += 1;
        if !skip {
            self.inner.token(kind, text);
        }
    }
}